Question

Which of the following has a constant of proportionality of 2?

y = 2x
y = x + 2
2y = x
y + 2 = 2x

Answer 1

Linear fonction's equation : y = ax

So only in y = 2x
2 is the constant of proportionality

Answer 2

Answer : y= 2x

When y is directly proportional to x then

y = kx where k is the constant of proportionality.

y = 2x , the value of k is 2. so 2 is the constant of proportionality.

y = x + 2, the equation is not in the form of y=kx

2y = x , $y= \frac{x}{2}$ so constant of proportionality k is $\frac{1}{2}$

y + 2 = 2x , y = 2x -2 is not in the form of y=kx